U.S. patent number 4,092,846 [Application Number 05/655,187] was granted by the patent office on 1978-06-06 for detection of liquid in a gas stream.
This patent grant is currently assigned to PPG Industries, Inc.. Invention is credited to Wilmer B. Graybill, Thomas C. Jeffery.
United States Patent |
4,092,846 |
Jeffery , et al. |
June 6, 1978 |
Detection of liquid in a gas stream
Abstract
Liquid if present in a gas stream is detected by expanding the
volume per unit weight of the gas in a vessel to the point where
liquid collects in the bottom of the vessel and weighing the
liquid.
Inventors: |
Jeffery; Thomas C. (Lake
Charles, LA), Graybill; Wilmer B. (Pittsburgh, PA) |
Assignee: |
PPG Industries, Inc.
(Pittsburgh, PA)
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Family
ID: |
24086425 |
Appl.
No.: |
05/655,187 |
Filed: |
February 4, 1976 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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523777 |
Nov 14, 1974 |
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256081 |
May 23, 1972 |
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Current U.S.
Class: |
73/29.01;
96/408 |
Current CPC
Class: |
G01N
5/00 (20130101); G01N 25/70 (20130101) |
Current International
Class: |
G01N
25/56 (20060101); G01N 5/00 (20060101); G01N
25/70 (20060101); G01N 033/00 () |
Field of
Search: |
;73/29,53,61.1R,73,76
;55/270,218,465,DIG.23 ;210/65,151 ;340/235,272 ;116/109 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Ciarlante; Anthony V.
Attorney, Agent or Firm: Grassi; Robert J.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This is a continuation of application Ser No. 523,777, filed Nov.
14, 1974 now abandoned which is a continuation-in-part of our
application entitled "Detection of Liquid in a Gas Stream", Ser.
No. 256,081, filed May 23, 1972 now abandoned.
Claims
We claim:
1. In the method wherein liquid chlorine is vaporized to produce a
stream of chlorine gas, the improvement comprising passing said
stream of chlorine gas through a vessel wherein liquid and vapor
are segregated and weighing said vessel and its contents to
determine whether liquid chlorine is present in said stream of
chlorine gas.
2. The method of claim 1 wherein said vessel has a sump to trap
liquid chlorine if present in said stream of chlorine gas.
3. The method of claim 2 wherein the weighing is performed
intermittently.
4. The method of claim 2 wherein the weighing is performed
continuously.
5. The method of claim 1 wherein a predetermined increase in weight
detected during said weighing initiates an alarm.
6. The method of claim 1 wherein a predetermined increase in weight
detected during said weighing causes the flow of said stream of
chlorine gas to be stopped.
7. An apparatus for vaporizing a liquid comprising a vaporizer
means to which that liquid is fed and means for supplying heat to
said vaporizer means, the combination therewith of apparatus for
producing a substantially liquid-free vapor stream comprising a
vessel, a line feeding fluid to said vessel, a line for removing
vapor from said vessel, means within said vessel for segregating
liquid from vapor, and means for determining the weight for said
vessel.
8. Apparatus as defined in claim 7, characterized in that said
apparatus further comprises means responsive to said weighing means
for activating an alarm when the weight of said vessel exceeds a
predetermined value.
9. Apparatus as defined in claim 7, characterized in that said
apparatus further comprises means responsive to said weighing means
for decreasing the rate at which liquid is fed to said vaporizer
means.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method and apparatus for detecting if
liquid is present in a gas, and for segregating the liquid from the
gas. Specifically, it concerns the method and apparatus for
adiabatically expanding the volume of a gas stream and/or reducing
the flow of the gas stream until liquid, if present, segregates
from the gas stream, and detecting the segregated liquid by
collecting and weighing it.
2. Description of the Prior Art
Detection of liquid and its removal from a gas stream is very
important, particularly in exothermic chemical reactions such as
chlorination, fluorination, etc., where liquid, if present in the
gas stream entering the reactor, causes explosions because of the
large amount of exothermic heat generated by reaction of the liquid
with the reactants. The detection and segregation of liquid in a
gas stream is also important in drying and evaporating operations,
for if liquid is present in a gas stream used for drying, then the
drying operation is prolonged and perfect drying may not occur.
Several methods are used to overcome these problems. In one method,
extra heat is added to the gas stream to vaporize any liquid
present; a method currently employed in chlorination reactions.
However, if the heat supply fails, then liquid may be present and
disastrous results may follow. In another method, baffles are used
to entrain any liquid particles present, as described by C. E.
Graham in U.S. Pat. No. 2,290,323, but baffles are not suitable for
early detection of the liquid, and furthermore elaborate baffle
systems are required when small amounts of liquid occur in a gas
stream. In another method, described by Crawford in U.S. Pat No.
2,268,442, gaseous water is chemically absorbed by a solid, such as
lithium iodide, to determine the amount present in the gas stream.
However, this technique is inapplicable where both gas and liquid
particles of the same chemical composition are present, as in
vaporized chlorine, for it cannot distinguish between the gas and
liquid because the solid absorbs both. These drawbacks are overcome
in the present invention which employs a relatively efficient,
simple, rapid detection and segregation of the liquid.
SUMMARY OF THE INVENTION
The liquid, if present in the gas stream, is detected by expanding
the volume occupied by unit weight of gas stream until the linear
speed of the gas stream is reduced in a sufficient amount to the
point where, the liquid concentrates in a portion of the gas stream
where it is detected by optical measurements, but preferably the
speed is reduced to the point where the liquid segregates from the
stream and is detected by the simple procedure of collecting it and
weighing it. Thus, a gas stream is passed through an apparatus
having a vessel constructed and arranged so that the volume of a
unit weight of the gas stream within the vessel is increased
relative to the volume of gas entering and leaving the vessel in
the amount sufficient to reduce the linear speed of the gas stream
in the vessel to the point where liquid, if present, segregates
from the gas and collects within the sump of the vessel. A means
such as a scale or other device continuously or intermittently
weighs the vessel to detect the presence of liquid by the weight
increase.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a chlorine vaporization unit equipped with the
device for detecting the presence of liquid chlorine.
FIG. 2 illustrates a vessel for segregating and collecting the
liquid, if present, supported on a scale connected to a warning
alarm.
FIG. 3 illustrates a vessel for segregating and collecting the
liquid, if present, supported on a scale connected to an automatic
valve for stopping the flow of gas when the liquid content reaches
a predetermined value.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
One of the principal forms in which materials are transported and
used in the chemicals industry is a stream of gas. It is usually
desired that such gas streams be free of liquid, but occasionally,
despite precautionary procedures practiced to prevent such an
occurrence, the gas stream becomes contaminated with unacceptable
amounts of liquid. In order to guard against the introduction of
the liquid-contaminated gas stream to a downstream process or
storage facility, the presence of liquid must first be detected.
The present invention which incorporates by reference the matter of
our application, `DETECTION OF LIQUID IN A GAS STREAM`, Ser. No.
256,081, filed May 23, 1972, provides for determining whether
liquid is present in a stream of gas by passing the stream of gas
through a vessel and weighing the vessel and its contents. Because
the vessel represents a constant volume, an increase in weight
represents an increase of the average density of the material
within the vessel. Moreover, because the differences in densities
of liquids and gases are generally quite large, the minor changes
in the density of a gas due to ordinary fluctuations in temperature
and pressure may be ignored, while the presence of a significant
amount of liquid can be detected easily. The vessel may have a sump
to trap liquid if present in the stream of gas. In fact, this is
the preferred mode of operation. The sump serves to accumulate
liquid, thereby increasing the sensitivity of the method.
Additionally, it is preferred that the cross-sectional area of the
vessel's interior which is normal to the direction of flow be
greater than that of the conduit supplying the stream of gas to the
vessel. This permits a reduction in linear velocity within the
vessel and allows segregation of the liquid and gaseous phases with
greater facility.
Weighing may be accomplished intermittently or continuously, but
the latter manner is preferred.
This invention is particularly suited for the detection of liquid
in a stream of gas where the stream of gas has been produced by the
vaporization of a liquid. While the vaporization of the liquid
ordinarily proceeds satisfactorily, occasionally unvaporized liquid
or condensate will be present in the line normally carrying the gas
stream from the vaporizer. Application of the principles of the
present invention serves to determine whether such liquid is
present in the line.
Of especial importance is the vaporization of liquid chlorine.
Large quantities of chlorine are shipped to their destinations in
the liquid state in order to reduce shipping costs. The liquid is
then vaporized to generate a stream of chlorine gas which is used
for its intended purpose, as for example, gas phase chlorinations
or oxychlorinations. The unknown introduction of liquid chlorine
into such process is usually undesirable since the liquid will
provide excessive amounts of chlorine to the system. Detection of
liquid chlorine in the line from the vaporizer is, therefore, of
considerable importance. By passing the stream of chlorine gas
through a vessel and weighing the vessel and its contents,
detection of the presence of liquid chlorine, if any, is easily
accomplished.
Any of the methods and apparatuses commonly employed to weigh
materials may be used to weigh the vessel through which the gas
stream is passed. Spring scales, beam scales, balances, flexible
beams, strain gauges, and load cells are examples of devices which
may be used to detect an increase in weight.
It is often convenient to allow a predetermined increase in weight
detected during weighing to initiate an alarm or cause the flow of
the stream of gas leaving the vaporizer to be stopped. Several
kinds of output can be employed from the weighing device. The
closing of a set of contact points can complete an electrical
circuit. A valve in a pneumatic system may be opened or closed by
the weighing device. The change in resistance of a strain gauge or
a load cell may be measured by a change in current or voltage in
accordance with known circuits using known principles such as a
Wheatstone bridge. Relays, transducers, and amplifiers may be used
where appropriate. The alarm is usually a bell, buzzer, gong,
siren, light, or similar device. The flow of the gas stream from
the vaporizer may be stopped directly, as for example, by a
solenoid valve or a pneumatically operated valve position in the
line leaving the vaporizer. In this case a pressure relief valve
can be used to prevent the build up of excessive pressures in the
vaporizer. Preferably, the source of heat to the vaporizer is also
cut off. The flow of gas stream from the vaporizer may be stopped
indirectly, as for example, by cutting off the supply of heat to
the vaporizer. Thus, a valve supplying steam may be closed or a
switch supplying electrical energy may be opened. Another manner of
indirectly stopping the flow of the gas stream is by shutting off
the flow of liquid chlorine entering the vaporizer. Two or more of
these methods may be employed together.
The method for detecting the presence of liquid in a gas is
illustrated in the vaporization of chlorine by the unit shown in
FIG. 1. Liquid chlorine or other liquified gas feeds through line 1
to the vaporizer 2, where steam from line 3 condenses and heats
steam dome 4, causing the liquid chlorine surrounding this dome to
vaporize and flow through line 9. The steam condensate is collected
in stream trap 5 and flows back to the steam generator or to sewer
through line 6. During start-up when dome 4 contains air or other
gas, valve 8 opens for the air to vent through line 7, and then
closes. The vaporized chlorine flows through line 9 and flexible
line 10 into vessel 11 and out of the vessel through flexible line
15 and line 16 to the point of its intended use.
Vessel 11 is supported by legs 12 upon weighing scale 13. When
chlorine gas enters the vessel through line 10, which has a
cross-sectional area smaller than that of vessel 11, it expands,
adiabatically, to that point where the linear speed of the gas
within the vessel is reduced in a sufficient amount to permit
liquid chlorine, if present, to concentrate in the lower portion of
the stream where it is detected. Preferably, the decrease in
gaseous flow within the vessel is such that the liquid falls from
the gas stream and collects within sump 18, causing a weight change
which scale 13 detects. The chlorine gas itself flows out through
line 15 which has a smaller cross-sectional area than the vessel
11. It is preferred that the collected liquid chlorine, after
weighing, feeds back batch-wise through valve 20, flexible line 22,
line 24, pump 26, and line 28 to the supply of liquid chlorine or
to disposal or other suitable destination. Vessel 11 has a baffle
14 or diverter positioned within the vessel for diverting the gas
flow downwardly into the vessel; otherwise, at high flow rates,
localized gas flow occurs at the top of the vessel between inlet
line 10 and outlet line 15.
In other embodiments, weighing scale 13, as shown in FIG. 2,
connects through line 34 to an alarm 36, so that when the weight
reaches a pre-set point 32, the alarm 36 warns that liquid is
present in the gas. Weighing scale 13, as shown in FIG. 3, connects
by line 40 to the automatic feed valve 42 so that when the weight
reaches a preset point 32 it signals valve 42 to shut off the feed
of liquid chlorine.
The specific embodiments of the invention described above, employ
the method of increasing the volume of a unit of gas until the flow
of gas is such that the liquid segregates out from the gas,
collecting the liquid and weighing it. In other embodiments of the
invention, the volume of the gas can be increased until the linear
speed of the gas stream is reduced to where the pull of gravity
upon the liquid particles is sufficiently greater than the
collision force of the gas molecules so that the liquid particles
concentrate in the lower portion of the gas stream and the increase
in concentration is detected by optical measurements, conductivity
measurements, etc.
Although chlorine vaporization is specifically shown, other gas
vaporization systems are amenable to the invention, such as
fluorine, bromine, or steam systems. For example, when steam is
wet, that is, liquid droplets of water are present in the steam,
these will segregate and be detected by the method and apparatus of
this invention. The invention is applicable to systems which
vaporize liquid by passing a gas inert to the liquid through the
liquid, for if liquid droplets are being carried within the stream
of gas, the steps of expanding the stream until the linear speed of
the gas is reduced to where the liquid concentrates in the lower
portion of the flowing stream and detecting this concentration
increase, or where the liquid segregates completely from the
stream, collecting the liquid and weighing it are readily
accomplished.
While the invention has been described with reference to specific
details of certain illustrative embodiments, it is not intended
that it shall be limited thereby except in so far as such details
appear in the accompanying claims.
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